Method of making a die cast cylinder for internal combustion engines



'Dec. 26, 1967 A F BAUER 3,359,615

METHOD OF MAKING A DIE CAST CYLINDER FOR INTERNAL COMBUSTION ENGINES Filed March 6, 1963 2 Sheets-Sheet 1 INVENTOR. ALFRED F'- BAUER l7 5 BY w ATTORNEYS A. F. BAUER 3,359,615 METHOD OF MAKING A DIE CAST CYLINDER FOR INTERNAL Dec. 26, 1967 COMBUSTION ENGINES Filed March 6, 1963 2 Sheets-Sheet 2 INVENTOR ALFRED F: BAUER BY a,

A' ToR NEY5 United States "Patent 3,359,615 METHOD OF MAKING A DIE CAST CYLINDER FOR INTERNAL COMBUSTION ENGINES Alfred F. Bauer, Toledo, Ohio, assignor to National Lead Company, New York, N.Y., a corporation of New Jersey Filed Mar. 6, 1963, Ser. No. 263,313 6 Claims. (Cl. 29156.4)

This invention relates to cylinders or housings for rotary piston internal combustion engines and to a method of making same. The invention is particularly directed to cylinders or housings which will permit higher engine outputs and much prolonged engine life. While the invention is of a special utility in connection with the trochoid cylinders or housings of so-called Wankel engines, it is useful in other engines as well where heat, pressure and corrosive fuel components create unusual problems.

In the rotary piston four-stroke cycle internal combustion engine of the Wankel type, the Walls of the trochoid housings are subject to extremely high localized temperatures and pressures. In an engine of this kind, combustion occurs repeatedly at a single area of the housing which never receives the benefit of cool gases between cycles as in a reciprocating engine. These engines operate at relatively high speeds so that the application of heat to the housing wall at the combustion point is virtually continuous. In the reciprocating four-cycle engine, on the other hand, the cylinder is scavenged between power strokes and the heat of combustion is dissipated to the exhaust system as well as to the engine water jacket so that there is ample opportunity to provide adequate cooling.

With the introduction of at least experimental work on the rotary piston engine in the United States the desirability of increased power output has become apparent. Such increased power output means that more fuel must be burned at each cycle, that more heat is created, and that the cooling problem becomes increasingly acute. Because of this, it has been proposed to die cast the trochoid housing in an aluminum alloy, to take advantage of the high heat conductivity of aluminum. Aluminum alloys, however, must operate at relatively low temperatures to maintain their physical properties and the castings must be so designed that the localized heat is adequately dissipated. This necessity has created a limitation on the size and power output of the engines. The primary object of the present invention is to remove this limitation and to provide a housing having greatly improved heat transfer characteristics and strength characteristics at the critical or crucial points of the trochoid housing.

In the rotary piston engine a pressure seal is used on the tips of the multi-lobe rotor which bears against the walls of the housing with a force that increases as the engine speed increases (see Wankel Patent 2,880,045). The motion of the rotor is not uniform, but accelerates and decelerates as the rotor turns relative to the driving shaft. Because of this, the centrifugal force of the rotor seals vary and certain areas of the housing tend to wear more than others. The wear resistance of the housing surface is an important factor in determining engine life. One of the objects of the present invention is to improve the wearing qualities of the housing surface against which the rotor seals bear while the engine is in operation.

Other objects and advantages of the invention will become apparent from the following specification, reference being made to the accompanying drawings, in which:

FIGURE 1 is a diagrammatic central, vertical, sec- "ice tional view of a portion of a die casting machine with the dies in place, ready for the injection of metal;

FIG. 2 is a central, vertical, sectional view of a reinforced trochoid housing constructed in accordance with the present invention;

FIG. 3 is an enlarged transverse sectional view of a portion of a housing wall showing a modified form of reinforcing element;

FIG. 4 is a perspective view of one form of reinforcing element shown in FIG. 2;

FIG. 5 is a perspective view of a coated die core ready for insertion in the die casting machine;

FIG. 6 is a central, vertical, sectional view of a completed housing having reinforcing elements applied in the combustion chamber area only; and

FIG. 7 is a sectional view taken on line 77 of FIG. 6.

The present invention comprises a method of die casting a trochoid housing for a rotary piston engine including the steps of providing a physical reinforcement at areas of high housing stress by overlaying those portions of a die core with reinforcing elements, covering said reinforcing elements with a metal having a higher melting point than the metal to be die cast, inserting the covered core in a die casting machine as a part of a die cavity, and casting metal of lower melting point such as aluminum or magnesium around and into intimate contact with the covered areas, whereby the reinforcing elements become cast into the housing. Said reinforcing elements may serve the dual purpose of (a) conducting heat away from the area of the casting in which they are embedded and (b) adding greatly to the strength of such area against deflection and distortion.

The method of the present invention further comprises the application of a micro-porous coating or covering to the die core which is transplanted to the housing by the die casting operation and which is subsequently electroplated for wear resistance or to impart other desirable surface properties to the housing. It has been found that a micro-porous coat of a ferrous or cuprous alloy, for example, accepts a chrome plate more readily and holds such plate more tenaciously than a dense non-porous body. A molybdenum coat or plate also has highly desira-ble surface characteristics. The surface properties of the housing are thus greatly improved.

In the drawings, the trochoid housing is indicated generally at 10 and includes cooling fins 11 die cast integral therewith in a pattern and spacing determined by the engine designer. If the housing is water cooled as in some engines, the fins will, of course, be replaced by water jackets. Inasmuch as the present invention pertains to the engine housing, no disclosure has been made of the rotor, gearing, bearings or other elements.

At the top of the housing 10, provision is made for the seating of a spark plug or fuel injector in a radial boss 12. If the rotor rotation is clockwise with respect to the housing in the position shown in the drawings, the part of the housing immediately beyond the spark plug or injector boss 12 represents an area at which combustion occurs. The intake and exhaust ports of the engine are not shown since they are usually disposed in one of the side cover plates that are bolted to the housing and are controlled by the face of the rotor. The exhaust ports occur at about around the housing from the combustion chamber. As above noted, the housing part that serves as the combustion chamber never receives the benefit of a flow of cooling gases as in a normal reciprocating fourstroke cycle engine. Therefore, the temperature of this part runs higher than the remainder of the housing and limits the power output of the engine by limiting the quantity of fuel that can be burned without destroying the housing. As more and more heat enters the cycle with 1 increased fuel the higher will be the operating tempera- 3 ture of the housing. If the housing is an aluminum alloy die casting, its physical properties will deteriorate as the temperature increases. The present invention is directed to a housing, and a method of making same, which overcomes the aforementioned difiiculty by reinforcing the housing at the critical area or areas.

The improved method of making the improved hous ing will now be described.

FIGURE 1 shows diagrammatically, a die for making the improved housing, in place in a die casting machine. The die includes a cover half 13, an ejector half 14 and side cores 15 and 16 to form the fins 11. A shot plunger 17 forces metal from a shot sleeve 18 through an appropriate gate 19 into the die cavity. A die core 20 is removably seated in one of the die halves, being shown in the ejector half and held in place by an extension 21 which fits immediately in a socket 22 in the die body. Ejector pins 23 are shown diagrammatically for removing a completed casting.

According to the present invention, the die core 20 is initially coated with a metal having a higher melting point than aluminum. This metal is preferably a ferrous alloy and is applied by a spray method so that as deposited, the, metal layer contains not only the ferrous metal but oxides thereof. The metal layer is designated generally 24. Brass or other copper containing alloy may also be deposited on the core in certain instances, particularly when the added step of electro-plating the interior of the housing is to be employed.

Following the application of the metal layer 24 to the core, reinforcing members are applied thereto. The reinforcing members may comprise structural shapes such as angles, bars, Ts or channel shapes as shown in FIG. 2 or may comprise a circumferentially extending wire 26 as shown in FIG. 3. A third form of structural reinforcing member comprises a corrugated sheet of expanded metal or perforated metal as shown in FIG. 5.

The structural shapes used as reinforcing members 25 may also be made of a ferrous metal. If such a metal is selected, the bars or shapes may be magnetized for temporary adherence to the metal layer 24. The core 20 with the reinforcing elements adhering thereto is then sprayed again with metal to unite the reinforcing elements to the layer 24. If the initial layer 24 is, for example, 0.020" thick, only a very thin layer of a few thousandths of an inch need be added to anchor the reinforcing elements in place. The metal layer that is applied over the reinforcing elements need only be thick enough to anchor them temporarily until the metal is die cast around the coated core. If the disposition of the reinforcing elements in the die with respect to the gate is such that the pressure of the incoming metal would tend to displace them, the added anchoring coat should be heavier.

If the wire wrap reinforcement is used as shown in FIG. 3, the reinforcing wire may be wound around the core 20 while it is still in the coating machine. Here again the wire is applied over a predetermined thickness of coating metal 24. and held in place by additional metal of the same or different composition. The wire is preferably of a ferrous alloy.

When using expanded metal reinforcement as shown in FIG. 5, the corrugated and perforated sheet designated 26 is attached to the coating by spraying additional coating metal around and over the segments, but not filling all of the grooves and interstices therein. By leaving the perforated sheet partially exposed, the die cast metal will be forced under and around the reinforcing segments as shown in the sectional view, FIG. 7. The reinforcement obtained by this form of the invention is especially advantageous for a localized area.

After the reinforcing segments or members have been applied to the core 20, the core is placed in the die, the shot made, and the completed casting removed as shown and described in my co-pending application Ser. No. 811,611.,now Patent No. 3,083,424. The metal coat 24 will 4 be found to transplant from the core 20 to form the inner wall of the housing 10. By reason of the presence of the reinforcing members, the strength of the housing 10 is greatly improved, and the improvement can be localized at the selection of the designer.

The running surface swept by the engine rotor is subject to wear by friction imposed by the rotor seals and it is desirable to improve the wearing qualities of this surface. It has been found that the metalized coating applied by spraying is micro-porous even though the interior is smooth to about 15 R.M.S. The porosity is very fine, but is sufficient to provide a very effective holding surface for plating of a desired friction-resisting metal such as chromium or molybdenum. Chrome plating of engine cylinders has been a common expedient in recent years, but in the past the plating has been applied directly to the cast metal. If the cylinder is cast in aluminum, it is more difficult to obtain a satisfactory plate than if the cylinder were to be cast in a ferrous metal. The present invention provides, in effect, an aluminum cylinder with a ferrous (or cuprous) face to be plated and has all of the desirable properties of cylinders of both metals. While the improvement of wearing qualities is of significant importance in the trochoid housing above described, it has also been found that the wearing qualities of a cylinder for a reciprocating engine can likewise be improved by chrome plating the microporous transplanted coat.

While the invention has been disclosed in conjunction With a specific form and disposition of the parts, and in conjunction with specific alloys for the coatings, it should be appreciated that numerous modifications and changes can be made therein without departing from the scope of the appended claims.

What I claim is:

1. The method of making a reinforced light metal cylinder for an internal combustion engine which includes depositing a coating of a metal having a higher melting point than the light metal on a core piece, applying reinforcing elements over said coating on at least those areas where high stress occurs during engine operation, depositing additional coating material over at least portions of said reinforcing elements to retain their position with respect to said core piece, introducing the core piece with the coating and reinforcing elements thereon into a die casting die, casting light metal around said core and reinforcing elements under die casting pressures to embed said reinforcing elements and to unite the light metal with the exposed surface of said coating, and stripping said casting from said core whereby said coating and reinforcing elements remain with said casting and said core can be returned for subsequent casting cycles.

2. The method defined in claim 1 in which the deposition of metal on said core piece leaves a micro-porous coating.

3. The method defined inaclaim 2 and subsequently chrome plating the exposed micro-porous surface of said light metal casting over the coating initially deposited on said core.

4. The method defined in claim 1 in which the application of reinforcing elements comprises wrapping wire over the coating, and holding the wire in place by additional coating material.

5. The method defined in claim 1 in which the reinforcing elements are disposed in the combustion chamber area of the resulting cylinder.

6. The method of making a reinforced light metal cylinder for an internal combustion engine which includes, depositing a coating of a ferrous metal alloy having a higher melting point than the light metal on a core piece, magnetizing magnetizable ferrous alloy reinforcing elements, applying said magnetized reinforcing elements over said coating on at least those areas where high stress occurs during engine operation, depositing additional coating material over at least portions of said reinforcing elements to ret in heir position with respect to said core piece, introducing the core piece With the coating and reinforcing elements thereon into a die casting die, casting light metal around said core and reinforcing elements under die casting pressures to embed said reinforcing elements and to unite the light metal with the exposed surface of said coating, and stripping said casting from said core whereby said coating and reinforcing elements remain with said casting and said core can be returned for subsequent casting cycles.

References Cited UNITED STATES PATENTS 6 Parker 138-140 Coatalen 138-140 Canfield et a1. 138-140 Jenkins 138-153 Van Deventer 29-1564 Kennison 138-153 Holben et al. 29-1564 Wankel et al. 123-8 Bauer 22-203 Bentele 123-8 X Lamm 123-8 JOHN F. CAMPBELL, Primary Examiner.

J. L. CLINE, F. T. SADTER, Assistant Examiners. 

1. THE METHOD OF MAKING A REINFORCED LIGHT METAL CYLINDER FOR AN INTERNAL COMBUSTION ENGINE WHICH INCLUDES DEPOSITING A COATING OF A METAL HAVING A HIGHER MELTING POINT THAN THE LIGHT METAL ON A CORE PIECE, APPLYING REINFORCING ELEMENTS OVER SAID COATING ON AT LEAST THOSE AREAS WHERE HIGH STRESS OCCURS DURING ENGINE OPERATION, DEPOSITING ADDITIONAL COATING MATERIAL OVER AT LEAST PORTIONS OF SAID REINFORCING ELEMENTS TO RETAIN THEIR POSITION WITH RESPECT TO SAID CORE PIECE, INTRODUCING THE CORE PIECE WITH THE COATING AND REINFORCING ELEMENTS THEREON INTO A DIE CASTING DIE, CASTING LIGHT METAL AROUND SAID CORE AND REINFORCING ELEMENTS UNDER DIE CASTING PRESSURES TO EMBED SAID REINFORCING ELEMENTS AND TO UNITE THE LIGHT METAL WITH THE EXPOSED SURFACE OF SAID COATING, AND STRIPPING SAID CASTING FROM SAID CORE WHEREBY SAID COATING AND REINFORCING ELEMENTS REMAIN WITH SAID CASTING AND SAID CORE CAN BE RETURNED FOR SUBSEQUENT CASTING CYCLES. 